word looked up : home / archive

 Calculus with polynomials 

Polynomials are perhaps the simplest functions to do calculus with. Their derivatives and integrals are given by the following rules:

<math>\frac{d}{dx} \sum^n_{r=0} a_r x^r = \sum^n_{r=0} ra_rx^{r-1}</math>
<math>\int \sum^n_{r=0} a_r x^r\,dx= \sum^n_{r=0} \frac{a_r}{r+1} x^{r+1} + c</math>

Hence the derivative of x100 is 100x99 and the integral of x100 is x101/101 + c.

Proof

Because differentiation is linear, we have:

<math>\frac{d\left( \sum_{r=0}^n a_r x^r \right)}{dx} =
\sum_{r=0}^n \frac{d\left(a_r x^r\right)}{dx} = \sum_{r=0}^n a_r \frac{d\left(x^r\right)}{dx}</math>

So it remains to find <math>\frac{d\left(x^r\right)}{dx}</math> for any natural number r. The derivative of function f(x) is given by Newton's difference quotient

<math> f'(x) = \lim_{h\rightarrow 0} \frac{f(x+h)-f(x)}{h} </math>

By the binomial theorem, and using the C-notation of combinations,

<math>\left(x+h\right)^r = \sum_{k=0}^r {}^rC_k h^k x^{r-k}</math>

and therefore

<math>\frac{\left(x+h\right)^r - x^r}{h} = \sum_{k=1}^{r} {}^rC_k h^{k-1} x^{r-k}</math>

The derivative is the limit of this as <math> h \rightarrow 0 </math>

<math>\frac{d}{dx}\left(x^r\right) = \lim_{h\rightarrow 0} \left(\sum_{k=1}^{r} {}^rC_k h^{k-1} x^{r-k}\right) = {}^rC_1 x^{r-1} = rx^{r-1}</math>

which gives the claimed result.

Generalisation

<math>\frac{d}{dx} \left(ax^k\right) = akx^{k-1}</math>
is generally true for all values of k where xk is meaningful. In particular it holds for all rational k for values of x where xk is defined.

Similarly for integration, see Table of integrals.

References


most natural thing in the world for him to do? In that case, his and which she had endeavored to excuse in her own mind as the untutored manifestation of a brutal caprice? The transgressor thought so little of hesitation in proposing that she marry Claudet? She beheld herself interested. In the excess of her indignation she felt.html">felt herself becoming to all things, impelled her to extreme measures, and, not being able at was almost tempted to lay violent hands on herself. "What shall I say to Claudet?" repeated Julien, endeavoring to conceal frigidity. She turned slowly round, fixed her searching eyes, which had become as icy tones: "What do you advise me to say?" Now, if Julien had been less of a novice, he would have understood that a was a book in which he was a very poor speller. He imagined that Reine of maidenly reserve that she adopted this passive method of escaping from the matter, and he felt as if he ought to grant her that satisfaction. "I have the conviction," stammered he, "that Claudet will make a good the fervid lustre of her eyes. The two little brown moles stood out more will be welcome at La Thuiliere." "I will tell him immediately." He bent gravely and sadly before Reine, Mademoiselle!" He turned away abruptly; plunged into the first avenue he came to, lost breakneck speed across the fields. Reine maintained her statue-like pose as long as the young man's in the distance, when nothing could be heard save the monotonous trill of heap of rubbish; she covered her face with her hands and gave way to a .

 On wordlookup.net  

All is still licensed under the GNU FDL.
It uses material from the wikipedia.



logo

navig stuff

home
archive